Draft control apparatus



Nov. 1, 1955 H. c. EDWARDS DRAFT CONTROL APPARATUS Filed April 2, 1952INVENTOR HOWARD C. EDWARDS m g I Z 00% W2 ATTORNEYS United States Patent0.

DRAFT CGNTROL APPARATUS Howard C. Edwards, Canton, Ohio, assignor, bymesne assignments, to John 'E. Miller, Canton, Ohio, as trusteeApplication April 2, 1952, Serial No. 280,053

6 Claims. (Cl. 230-95) This invention relates to draft control, and moreparticularly relates to the draft control of household heating such asfurnaces, space heaters, hot water heaters, and overhead unit heaters,although the control may be used in other environments.

In the common heating installation the smoke pipe which carries theproducts of combustion from the furnace to the chimney is ordinarilyprovided with a check damper Which when closed prevents exterior airfrom entering the pipe and when open allows air to be drawn in from theoutside to reduce the draft at the furnace, the reduction being inaccordance with the amount ofdraft and the extent to which the damperhas been opened. Should the chimney be cold when the fire in the furnaceis started or a demand for heat is made, the opening of the damper wouldhinder the initial establishment of a draft in the chimney due to thefact that any air that is sucked in through the damper would berelatively cool and thus delay an increase in the temperature and draftin the chimney. With such constructions, even with the damper closed,when the chimney is cold and the fire in the furnace is started, or ademand for heat is made, the lack of draft in the chimney impedes theflow of the products of combustion through the smoke pipe and up thechimney. As a result, the impeded products of combustion build up backpressure in the furnace and this in turn impedes the inflow ofcombustion supporting air and results in imperfect combustion and thecreation of smoke and soot which frequently finds its way into the roomthrough cracks in the furnace and damper.

To ameliorate these objectionable conditions it has been proposedheretofore to force outside air into the smoke pipe in a stream directedtoward the chimney with the view of inducing the products of combustionto flow into the stack faster and thereby stop the tendency for backpressure in the furnace to build up and to heat the chimney quicker. Anexample of an arrangement designed to that end may be found in PatentNo. 2,164,880 of G. A. Merkt issued July 4, 1939.

My present invention has for an object an improvement over said priorconstructions in many respects not only in functioning and operation butalso in structure whereby said improvements in operation and results areaccomplished.

It is also well known that it is objectionable to have too strong adraft in the chimney, as frequently occurs after the fire has been goingin the furnace for some time, and the damper in the smoke pipe is notproperly adjusted. It is an object of this invention to provide aconstruction which not only operates to increase the draft when thechimney is relatively cool but also to reduce or dampen the draft whenthe chimney becomes so hot as to have objectionably strong draft. Theoptimum draft in chimneys of household furnaces is in about the range of0.05 to 0.07 inch of water; and a more specific object of this inventionis to provide a draft controlling device or apparatus which will quicklybuild up chimney pressure within that range when thefurnace is firstlighted or when- 2 ever there is a demand for heat and will maintain thedraft pressure within that range during the entire time the furnace fireis burning.

I have discovered that cold turbulent gases in the chimney where thegases enter the chimney from the smoke pipe interferes with the flowfrom the smoke pipe and thus interferes with the establishment of aproper draft in the chimney. Such turbulence and back pressure isparticularly noticeable in furnaces having gun type oil burners where itcauses severe pulsating. Accordingly another object of my invention isto provide a draft controlling device of the character stated above andwhich is so constructed that it will not cause turbulence of the gasesin the chimney where they are received from the smoke pipe.

During recent years there has been an increasing use of overhead unitheaters, ordinarily gas fired, in the remodeling of old buildingswithout central heating facilities, or in which it is not desirable toinstall new central heating equipment. The unit heaters ordinarilyexhaust through a pipe extending through a wall or window and are notprovided with a chimney. An important object of this invention is toprovide draft control apparatus for such unit heaters which will insureproper discharge of the products of combustion from the room in whichthe heater is used.

Another object of this invention is to provide a draft controllingdevice of the character stated above and which is of simple, durable andinexpensive construction, is simple and easy to install and is quiet,reliable and efiicient in operation.

A further object of this invention is to provide a draft controllingconstruction of the character described and which construction permitsthe adaptation of the invention to smoke pipes of any one of a number ofdifferent diameters.

The smoke pipes of household furnaces are usually only from 30 to 60inches in length; and a still further object of this invention is toprovide a draft controlling device of the character stated and which canbe used with and installed on such household furnace smoke pipes withoutdetracting from the efliciency and functioning of the heating device.

Other objects of this invention will be in part obvious and in partpointed out hereinafter.

In accordance with this invention there is an apparatus or device whichmay be installed conveniently in a smoke pipe which leads from a furnaceto a chimney for the furnace and which device has parts outside of thesmoke pipe and parts inside of the smoke pipe. The device in combinationwith the smoke pipe provides means for causing an annular stream of airto flow from an intermediate point in the smoke pipe toward the chimneyin such a way that the annular stream of air converges to an apex beforereaching the chimney, thus constituting means for accelerating the flowof the products of combustion in the smoke pipe to the chimney and atthe same time providing a space of suflicient length between said apexand the chimney to cause turbulence occasioned by the air stream tosubside and to avoid turbulence in the chimney where the smoke pipedischarges into the chimney. The parts of the draft control device areso shaped, dimensioned and relatively positioned as to accomplish theabove and to provide means for quickly elevating the draft pressure whenthe chimney is cool and the furnace fire first lighted or whenever thereis a demand for heat and to provide means for maintaining the stackdraft pressure at about the range of 0.05 to 0.07 inch of water whilethere is a demand for heat from the furnace, as will be pointed out morein detail hereinafter.

My invention takes advantage of the law of aerodynamics whereunder therate of flow of a stream of air can be accelerated by introducing intosaid air stream another air stream flowing in the same direction at a'greater velocity. In short in accordance with my invention I provide anapparatus or device associated and combined with a smoke pipe of afurnace and which includes means for introducing a stream of air intothe smoke pipe, means for establishing the size of the air stream whereit is discharged into the stream of combustion products flowing throughthe smoke pipe, means for establishing the velocity of the air stream atsaid point, and means for causing the air stream to flow in a certaindirectional formation or shape in the smoke pipe, all so constructed,arranged and coordinated that when the stack draft is undesirably lowthe introduced air stream will act on the combustion products in thesmoke pipe in such a way as to accelerate their rate of flow from thefurnace to the chimney and when the draft in the chimney is undesirablyhigh the introduced air stream will dampen or decelerate the velocity ofthe flow of the combustion products passing through the smoke pipe fromthe furnace to the chimney.

This invention accordingly consists in the features of construction,arrangement of parts, combinations of elements and dimensionalrelationship of parts which will be more clearly described hereinafterand the scope of the application of which will be set forth in theclaims that follow.

In order that a clearer understanding of this invention may be hadattention is hereby directed to the accompanying drawings, forming apart of this application and illustrating certain possible embodimentsof this invention and in which:

Figure l is a longitudinal sectional view of a section of smoke pipeequipped with a draft control embodying this invention, the blowerassembly being shown in elevation and the furnace, an adjacent length ofsmoke pipe and chimney being indicated by dot and dash lines;

Figure 2 is a transverse sectional view thereof and is taken on the line2-2 of Figure 1;

Figure 3 is a transverse sectional view thereof and is taken on the line33 of Figure l; and

Figure 4 is a diagrammatic view of certain parts with certainmeasurements indicated thereon.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

My invention is applicable to smoke pipes of different diameters, butfor the purpose of illustrating one possible embodiment of thisinvention we will assume that the drawings accompanying this applicationshow my invention applied to a smoke pipe having a diameter of 6 inches.

Referring to the drawings there is shown or indicated therein a furnaceF, a chimney S, a smoke pipe section 10 with which my draft controldevice is associated and combined, and a smoke pipe section P bridgingthe space between the furnace end of the smoke pipe section 10 and thefurnace. Obviously, two lengths of smoke pipe are not necessarilyrequired since the draft control device may be associated and combinedwith a smoke pipe which extends all the way from the furnace to thechimney. The reason a two-section smoke pipe is indicated in thedrawings is to illustrate that a unit comprising a smoke pipe section,such as 10, with my draft control device asso ciated and combinedtherewith may be made and installed in heating installations in whichthe distance between the furnace and the chimney are not the same. Inhousehold furnace installations the distance between the furnace and thechimney is usually between 30 to 60 inches. Because of this shortdistance, certain dimensions must be controlled within narrow limits ifan acceptable efliciency of operation is to be obtained. In some thedistance is more and in some less. Therefore by installing the draftcontrol mechanism on a relatively short section of smoke pipe, forinstance one 27 inches or so long, the draft control unit may beinstalled by adding, if required, a second section of smoke pipe of theproper length to connect the furnace end of the control unit to thefurnace.

Within the smoke pipe section 10 are two circular pipelike members 11and 12, the member 11 being toward the furnace end of pipe section 10and forming with the adjacent wall of the pipe section 10 one section orpart A of a plenum chamber therebetween; and the other member 12 beingpositioned to extend from the discharge end of member 11 toward thechimney. The member 11 is formed at its end toward the chimney with aflat annular portion 13 which seats against and about the inside of thesmoke pipe 10 and is secured thereto and the opposite end of member 11is formed to have a narrow axially extending annular lip 14. The Wall 15of member 11 has slight convex curvature from the portion 13 of member11 to the lip portion 14. For a smoke pipe of 6 inch diameter acurvature having a radius of approximately 33 /2 inches is preferred.The center of curvature is toward the stack slightly from the lip 14 inorder that the member 11 converges throughout its length. In the 6" sizeshown, the center of curvature will be about /2 inch toward the stackfrom the lip 14. The purpose and functioning of this curvature will bepointed out more fully hereinafter. The furnace end of section 11 isshown to be about 2 inches within the end of smoke pipe 10.

The end of the member 12 nearest the member 11 is formed with an annularshort nozzle 16 which tapers outwardly toward the member 11, overlapsthe lip 14 and has its extremity seated against and about the inside ofthe smoke pipe 10. The opposite end 17 of member 12, that is the endtoward the chimney, also seats about and against the inside of the smokepipe 10. The wall portion 18 of the member 12 tapers outwardly from thenozzle 16 to the outer end of member 12. From the hump 19 where the wall18 joins the chimney end of nozzle 16, the wall 18 has a slight convexcurvature, for instance a radius of about 33 /2 inches, and this curvedportion of the wall 18 extends for about 2 /2 inches from the hump 19toward the stack and then the wall 18 tapers straight to its end 17. Thecenter of curvature is spaced so the member 12 expands continually fromits minimum diameter at hump 19.

A hole is cut through the side of the smoke pipe 10 at the plenumchamber A and a hood 20 is fastened, as by welding to the smoke pipe andcovers this hole. The interior of the hood opens into the plenum chamberA and provides another part or section A of the plenum chamber which iscomposed of both plenum chamber sections A and A. The hood 20 has aninlet opening 21 and an assembly of blower 22, driving motor 23 and airdischarge duct 24 is mounted on the hood with the discharge duct at thehood inlet opening 21 so that the blower forces air under pressure intothe plenum chamber AA. The securing of the blower-motor assembly to thehood may be accomplished by fastening, as by welding, one web of anannular angle iron 25 about the end of the duct and securing the otherweb of the angle iron 25 to the hood about its opening, as by bolts 26.

In operation the blower 22 forces air under pressure into the plenumchamber AA. The curved wall 15 and lip 14 of section 11 cause all theflue gases from the furnace to be moving in a direction substantiallyparallel with the axis of the smoke pipe at the time it firstintermingles with the air from the nozzle 16. The nozzle 16 will deflectthe air striking it in a definite and closely confined direction. Theangular relation of the annular nozzle 16 to the axis of the smoke pipe10 is such that the annular stream of air flowing from the nozzleconverges to an apex, indicated at X, at which point the air projectedfrom the different points about the annular nozzle intermingles with theproducts of combustion in the smoke pipe and any turbulence that may bepresent dies out. The angle of the nozzle 16 is such that when combinedwith the convexly curved members 11 and 12, said apex X of the airstream is a sufficient distance in advance of the chimney opening as toinsure the absence of substantially any turbulence where the smoke pipedischarges into the chimney.

In order to obtain satisfactory efliciencies when installed in theaverage heating unit, itis essential that certain dimensions becontrolled within critical limits. Both the sections 11 and 12 should becurved about a radius ranging from about 20 to 40 inches at their endsadjacent one another. The distance from lip 14 to the outer Wall smokepipe 10 should range from about Zia" for a 6" smoke pipe to about /8"for a smoke pipe. The distance from the hump 19 to the wall of the smokepipe should be about $1 less. The angle between the nozzle 16 and thewall of the smoke pipe should be between 20 and 40 and preferably isapproximately 27. The combination of the convex surfaces of the twosections and the annular nozzle at the minimum cross section of theapparatus within the limitations described eliminates the turbulencewhich would be caused by the apex X being within the chimney.

For optimum performance, the area of the annual opening should besubstantially the same as the discharge area of the blower. In the usualdomestic installation, that will mean a range from about 3 /2 to 7 /2square inches. Since the capacity of the blower will be varied fromabout 50 to 300 cubic feet per minute, depending on the size of thefurnace and chimney, there will be a range within which the annular areamay vary. Ordinarily, the air supplied by the blower will be about 30%of the volume of the flue gases entering the smoke pipe 10, but may varyfrom about 25% to as much as 60%.

A rough chart showing suggested data to be followed for smoke pipes ofseveral different diameters issubmitted as follows:

Diameter of smoke pipe 6 7" 8" 9 10 Length of smoke pipe sec 1 tion"inches" 17% 18% 21 22 24 Length of Section 11. do 5 m; 5% 6% 6% 6%Length of Section 12.. do 6 16 8% 1034s 11 11 Spacing 11,? see Fig. 4

do is a Ms %2 Spacing b, see Fig. 4 A w n 9 0--.- B 6 6 Spacing 0, seeFig. 4 A A do %6 Me 364 %2 952 Discharge area at nozzle in squareinches: 1

The discharge area at the nozzle can be varied in accordance with thecapacity of the blower, L" indicating the lower limits and H the upperlimits.

In operation, when the usual thermostat turns on the heating unit, ifthe heating units is the ordinary gas or oil unit suitable connections,not shown, will close the circuit to the motor 23 of the blower 22 andstarts the blower. In a coal furnace, the motor 23 may be electricallyconnected with the stoker motor, or in a hand-fired unit mechanicallyconnected with the usual draft controls. The air from the blower isdischarged into the plenum chamber AA and thence flows outwardly throughthe nozzle 16 into the space defined by member 12. The rapid flow of airfrom nozzle 16 immediately provides a draft in member 11 and tends todraw products of combustion from the furnace F through the smoke pipe P.Thus even though the chimney S has not been heated, suflicicnt draft isprovided to prevent back pressure in the furnace with the resultantblowing of soot throughout the house.

After the burner has been in operation for some time the chimney S willbe hot and tend to increase the natural draft above the desired range.The air discharged from the blower counteracts this tendency in tworespects. It will decrease the temperature of the gases in the stack andthereby decrease the natural draft. In addition, the added airintroduced into the chimney by the blower causes increased pressure dropin the chimney with a resultant diminishing of the draft. Hence, theapparatus of this invention provides a stabilizing influence increasingthe draft to the desired range when the natural draft is low anddecreasing the draft to the proper value after the furnace has reachedits normal operating temperature.

By following the directions and instructions given above, a draftcontrol may be constructed and installed in a smoke pipe leading betweena furnace and a chimney and which will result in the stack draft beingbuilt up quickly to at least 0.05 inch of water when the furnace isfirst lighted or a demand for heat is made and will result in the stackdraft remaining at between 0.05 and 0.07 inch of water during all of thetime the heating unit is on. A device constructed and installed inaccordance with the above disclosure accomplishes all of the objects ofthe invention stated hereinbefore.

It will be appreciated that the device herein described results in aminimum obstruction to flow of flue gases, the cross sectional area atlip 14 being only slightly less than the area of the smoke pipe, and thesurfaces being smooth and unobstructed. With this structure a maximumefliciency, as measured by the ratio of cubic feet of gases entering thesmoke pipe 10 to the cubic feet of air supplied by the blower, isobtained. Since the air supplied by the blower usually will be slightlywarm air from the basement, and is in addition to the combustion air, ahigh efliciency is essential.

However, as many different embodiments of this invention could be madeand many changes could be made in the above construction withoutdeparting from the scope of this invention, it is understood that allmatter contained in the above description or shown in the accompanyingdrawings be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A draft inducing unit for heating apparatus, comprising a pipesection adapted to be interposed between the exhaust of a heating deviceand a flue, a venturi assembly in said section, including a compressionmember constricted at its outlet end, and a separate, coaxial expansionmember, constricted at its inlet end, the adjacent constricted ends ofsaid members being separated longitudinally to define a restrictedperipheral slot, opening to the interior of said venturi assembly, theinlet and exhaust ends respectively, of said members being oppositelydirected and flaring into sealed contact with said pipe section, anaxially converging lip formed on the inlet end of said expansion memberwhich terminates at its outer edge, in sealed contact with said pipesection and completely overlies said slot and the constricted end ofsaid compression member, said pipe section being concentric with andspaced radially outwardly from said compression member to form with thelatter, the annular boundary walls of a plenum chamber in said pipesection, surrounding said compression member substantially from end toend and having an annular discharge mouth directed toward said lip andcommunicating therethrough, with said restricted slot, and a bloweroperatively connected to the intake end of said chamber.

2. A unit as claimed in claim 1, wherein the walls of said compressionmember and expansion member are concave in cross-sectional profile.

3. A draft inducing unit for heating apparatus, comprising an annularpipe section adapted to be interposed between the exhaust of a heatingdevice and a flue, and forming the outer boundary of a plenum chambercoaxial with said pipe section, a coaxial compression tube, secured atits inlet end to the pipe section and forming the inner peripheralboundary of said plenum chamber, its discharge end having convergingwalls which form a restricted passageway, concentric with the pipesection, said plenum chamber having an annular outlet surrounding thedischarge end of said compression tube, a funnelshaped flange, theflaring outer edge of which overlies the discharge end of saidcompression tube in spaced relation thereto and is sealed to said pipesection, to form a converging throat, an expansion tube coaxial withsaid compression tube and spaced longitudinally therefrom, saidexpansion tube being connected at its inlet end to the throat of saidflange and flaring towards its opposite end into sealed engagement withsaid pipe section, the spaced adjacent ends of said tubes forming arestricted annular slot lying within the confines of the funnel-shapedflange and placing the plenum chamber outlet in communication with theinterior of said compression and expansion tubes, and a bloweroperatively connected to the inlet end of said chamber.

4. A draft inducing unit for heating apparatus, including a cylindricalpipe section adapted to be interposed between the exhaust of a heatingdevice and a flue, a venturi assembly in said pipe section, comprising agradually restricted, flue gas compression nozzle, and a coaxial,truncated, flue gas expansion cone, said pipe section being concentricand co-extensive with said nozzle, and spaced radially outwardly fromthe latter to form therewith the defining annular walls of a plenumchamber surrounding and co-extensive with said compression nozzle, therestricted discharge extremity of said nozzle being directed toward saidcone in a line substantially parallel with the axis of said nozzle andcone and spaced immediately in advance of the restricted inlet extremityof said cone, to form a restricted annular slot leading to the interiorof said venturi assembly, a funnel-shaped flange contiguous with saidinlet extremity of said cone, with its diverging wall overlying saidslot and terminating in sealed engagement with said pipe section to forma converging boundary wall for the adjacent exhaust end of said plenumchamber, and a blower operatively connected to the intake end of saidplenum chamber.

5. A draft inducing unit for heating apparatus, including a cylindricalpipe section adapted to be interposed between the exhaust of a heatingdevice and a flue, a venturi assembly in said pipe section, comprising agradually restricted, flue gas compression nozzle, and a coaxial,truncated, flue gas expansion cone, said pipe section being concentricand co-extensive with said nozzle, and spaced radially outwardly fromthe latter to form therewith the defining annular walls of a plenumchamber surrounding and co-extensive with said compression nozzle, therestricted discharge extremity of said nozzle being directed toward saidcone in a line substantially parallel with the axis of said nozzle andcone and spaced immediately in advance of the restricted inlet extremityof said cone, to form a restricted annular slot leading to the interiorof said venturi assembly, a funnel-shaped flange contiguous with saidinlet portion of said cone, with its diverging wall surrounding saidslot and overlying the restricted extremity of said nozzle, terminatingin sealed engagement with said pipe section, said flange forming withthe discharge extremity of said nozzle, respectively converging walls ofan annular mouth opening from the plenum chamber into said expansioncone, immediately in advance of the restricted inlet extremity thereof,and a blower operatively connected to the intake end of said chamber.

6. A draft inducing unit for heating apparatus, comprising a cylindricalpipe section adapted to be interposed between the exhaust of a heatingdevice and a flue, a venturi assembly in said pipe section, comprising agradually restricted flue gas compression nozzle, and a coaxial,truncated, flue gas expansion cone, said pipe section being concentricand coextensive with said nozzle, and spaced radially from the latter toform therewith the defining walls of a plenum chamber having its maximumannular cross-sectional area adjacent the restricted end of said nozzle,the restricted discharge extremity of said nozzle being directed towardand substantially parallel with the axis of said nozzle and cone, andspaced immediately in advance of the restricted inlet extremity of saidcone, to form a restricted annular slot leading to the interior of saidventuri assembly, a funnel-shaped flange contiguous with said inletextremity of said cone, with its diverging wall overlying said slot andterminating in sealed engagement with said pipe section to form aconverging boundary wall for the adjacent exhaust end of said plenumchamber, and a blower operatively connected to the intake end of saidchamber.

References Cited in the file of this patent UNITED STATES PATENTS542,864 Thomas July 16, 1895 1,604,271 Friedman Oct. 26, 1926 1,612,838Schultz Ian. 4, 1927 1,942,048 Clark Jan. 2, 1934 2,111,266 Hopkins Mar.15, 1938 2,361,861 Masowich Oct. 31, 1944 2,584,326 Campbell Feb. 5,1952 FOREIGN PATENTS 7,127 Germany Jan. 21, 1880

